In a typical inboard/outboard or inboard marine propulsion system, hot exhaust gases from engine cylinders discharge into a water jacketed exhaust manifold which directs the hot exhaust gases into a water jacketed exhaust elbow. The exhaust elbow normally has a generally vertical intake exhaust passage, and then bends around to a slightly downward sloping discharge exhaust passage. The hot exhaust gases flow into the exhaust elbow through the intake passage and exit the elbow through the exhaust discharge passage. Cooling water from the engine inputs the exhaust elbow water jacket from the same side as the exhaust intake and generally flows through the water jacket to the exhaust discharge where the coolant water is mixed with the hot exhaust gases. By mixing the coolant water with the exhaust gases, the exhaust gases are cooled. The mixture of exhaust gases and coolant water is then typically discharged through an exhaust bellows or exhaust tube and then through the transom, or the propeller torpedo, or the like.
It is sometimes desirable to discharge the mixture of cooled exhaust gases and spent coolant water through the transom of the boat above the surface of the water. Discharging below the water surface tends to create an exhaust back pressure which, under certain high performance conditions, can reduce the power output of the propulsion system. In high performance applications, it is also desirable to reduce the creation of exhaust back pressures during acceleration.
In systems where the exhaust tube passes through the transom of the boat to discharge the cooled exhaust gases and spent coolant water above the surface of the water (i.e. through-transom exhaust systems), water ingestion through the exhaust system back into the engine can be a significant problem. In through-transom exhaust systems, exhaust pressure pulsations due to reciprocating piston movement and valve overlap tend to suck water within the exhaust tube back into the engine. Water or moisture actually travels backwards into the interior of the exhaust passage within the elbow in a pulsating manner and eventually back into the engine. The pulsating water ingestion becomes more pronounced as engine size increases, especially in propulsion systems having little or no exhaust back pressure. This is typically true of high performance marine propulsion systems having through-transom exhaust systems.
Copending U.S. patent application Ser. No. 08/512,026, now U.S. Pat. No. 5,644,914, issued on Jul. 8, 1997, entitled "Exhaust Pressure Pulsation Control Apparatus for Marine Propulsion System" by Gregory B. Deavers, Loren T. Powers, and George E. Brown, assigned to the assignee of the present application and incorporated herein by reference, discloses an apparatus that eliminates exhaust pressure pulsation water ingestion without creating back pressure in the exhaust system. The apparatus disclosed in the above referenced copending patent application is especially useful in through-transom exhaust systems, or in other exhaust systems in which the cooled exhaust gases and spent coolant water are discharged above the surface of the water. The apparatus attenuates pressure pulsations in the exhaust system when placed at the proper location within the exhaust tube downstream of the exhaust elbow.